compiler/rustc_passes/src/loops.rs

   1 use Context::*;
   2
   3 use rustc_errors::{struct_span_err, Applicability};
   4 use rustc_hir as hir;
   5 use rustc_hir::def_id::LocalDefId;
   6 use rustc_hir::intravisit::{self, Visitor};
   7 use rustc_hir::{Destination, Movability, Node};
   8 use rustc_middle::hir::map::Map;
   9 use rustc_middle::hir::nested_filter;
  10 use rustc_middle::ty::query::Providers;
  11 use rustc_middle::ty::TyCtxt;
  12 use rustc_session::Session;
  13 use rustc_span::hygiene::DesugaringKind;
  14 use rustc_span::Span;
  15
  16 #[derive(Clone, Copy, Debug, PartialEq)]
  17 enum Context {
  18     Normal,
  19     Loop(hir::LoopSource),
  20     Closure(Span),
  21     AsyncClosure(Span),
  22     LabeledBlock,
  23     AnonConst,
  24 }
  25
  26 #[derive(Copy, Clone)]
  27 struct CheckLoopVisitor<'a, 'hir> {
  28     sess: &'a Session,
  29     hir_map: Map<'hir>,
  30     cx: Context,
  31 }
  32
  33 fn check_mod_loops(tcx: TyCtxt<'_>, module_def_id: LocalDefId) {
  34     tcx.hir().deep_visit_item_likes_in_module(
  35         module_def_id,
  36         &mut CheckLoopVisitor { sess: &tcx.sess, hir_map: tcx.hir(), cx: Normal },
  37     );
  38 }
  39
  40 pub(crate) fn provide(providers: &mut Providers) {
  41     *providers = Providers { check_mod_loops, ..*providers };
  42 }
  43
  44 impl<'a, 'hir> Visitor<'hir> for CheckLoopVisitor<'a, 'hir> {
  45     type NestedFilter = nested_filter::OnlyBodies;
  46
  47     fn nested_visit_map(&mut self) -> Self::Map {
  48         self.hir_map
  49     }
  50
  51     fn visit_anon_const(&mut self, c: &'hir hir::AnonConst) {
  52         self.with_context(AnonConst, |v| intravisit::walk_anon_const(v, c));
  53     }
  54
  55     fn visit_expr(&mut self, e: &'hir hir::Expr<'hir>) {
  56         match e.kind {
  57             hir::ExprKind::Loop(ref b, _, source, _) => {
  58                 self.with_context(Loop(source), |v| v.visit_block(&b));
  59             }
  60             hir::ExprKind::Closure { ref fn_decl, body, fn_decl_span, movability, .. } => {
  61                 let cx = if let Some(Movability::Static) = movability {
  62                     AsyncClosure(fn_decl_span)
  63                 } else {
  64                     Closure(fn_decl_span)
  65                 };
  66                 self.visit_fn_decl(&fn_decl);
  67                 self.with_context(cx, |v| v.visit_nested_body(body));
  68             }
  69             hir::ExprKind::Block(ref b, Some(_label)) => {
  70                 self.with_context(LabeledBlock, |v| v.visit_block(&b));
  71             }
  72             hir::ExprKind::Break(break_label, ref opt_expr) => {
  73                 if let Some(e) = opt_expr {
  74                     self.visit_expr(e);
  75                 }
  76
  77                 if self.require_label_in_labeled_block(e.span, &break_label, "break") {
  78                     // If we emitted an error about an unlabeled break in a labeled
  79                     // block, we don't need any further checking for this break any more
  80                     return;
  81                 }
  82
  83                 let loop_id = match break_label.target_id {
  84                     Ok(loop_id) => Some(loop_id),
  85                     Err(hir::LoopIdError::OutsideLoopScope) => None,
  86                     Err(hir::LoopIdError::UnlabeledCfInWhileCondition) => {
  87                         self.emit_unlabled_cf_in_while_condition(e.span, "break");
  88                         None
  89                     }
  90                     Err(hir::LoopIdError::UnresolvedLabel) => None,
  91                 };
  92
  93                 if let Some(Node::Block(_)) = loop_id.and_then(|id| self.hir_map.find(id)) {
  94                     return;
  95                 }
  96
  97                 if let Some(break_expr) = opt_expr {
  98                     let (head, loop_label, loop_kind) = if let Some(loop_id) = loop_id {
  99                         match self.hir_map.expect_expr(loop_id).kind {
 100                             hir::ExprKind::Loop(_, label, source, sp) => {
 101                                 (Some(sp), label, Some(source))
 102                             }
 103                             ref r => {
 104                                 span_bug!(e.span, "break label resolved to a non-loop: {:?}", r)
 105                             }
 106                         }
 107                     } else {
 108                         (None, None, None)
 109                     };
 110                     match loop_kind {
 111                         None | Some(hir::LoopSource::Loop) => (),
 112                         Some(kind) => {
 113                             let mut err = struct_span_err!(
 114                                 self.sess,
 115                                 e.span,
 116                                 E0571,
 117                                 "`break` with value from a `{}` loop",
 118                                 kind.name()
 119                             );
 120                             err.span_label(
 121                                 e.span,
 122                                 "can only break with a value inside `loop` or breakable block",
 123                             );
 124                             if let Some(head) = head {
 125                                 err.span_label(
 126                                     head,
 127                                     &format!(
 128                                         "you can't `break` with a value in a `{}` loop",
 129                                         kind.name()
 130                                     ),
 131                                 );
 132                             }
 133                             err.span_suggestion(
 134                                 e.span,
 135                                 &format!(
 136                                     "use `break` on its own without a value inside this `{}` loop",
 137                                     kind.name(),
 138                                 ),
 139                                 format!(
 140                                     "break{}",
 141                                     break_label
 142                                         .label
 143                                         .map_or_else(String::new, |l| format!(" {}", l.ident))
 144                                 ),
 145                                 Applicability::MaybeIncorrect,
 146                             );
 147                             if let (Some(label), None) = (loop_label, break_label.label) {
 148                                 match break_expr.kind {
 149                                     hir::ExprKind::Path(hir::QPath::Resolved(
 150                                         None,
 151                                         hir::Path {
 152                                             segments: [segment],
 153                                             res: hir::def::Res::Err,
 154                                             ..
 155                                         },
 156                                     )) if label.ident.to_string()
 157                                         == format!("'{}", segment.ident) =>
 158                                     {
 159                                         // This error is redundant, we will have already emitted a
 160                                         // suggestion to use the label when `segment` wasn't found
 161                                         // (hence the `Res::Err` check).
 162                                         err.delay_as_bug();
 163                                     }
 164                                     _ => {
 165                                         err.span_suggestion(
 166                                             break_expr.span,
 167                                             "alternatively, you might have meant to use the \
 168                                              available loop label",
 169                                             label.ident,
 170                                             Applicability::MaybeIncorrect,
 171                                         );
 172                                     }
 173                                 }
 174                             }
 175                             err.emit();
 176                         }
 177                     }
 178                 }
 179
 180                 self.require_break_cx("break", e.span);
 181             }
 182             hir::ExprKind::Continue(destination) => {
 183                 self.require_label_in_labeled_block(e.span, &destination, "continue");
 184
 185                 match destination.target_id {
 186                     Ok(loop_id) => {
 187                         if let Node::Block(block) = self.hir_map.find(loop_id).unwrap() {
 188                             struct_span_err!(
 189                                 self.sess,
 190                                 e.span,
 191                                 E0696,
 192                                 "`continue` pointing to a labeled block"
 193                             )
 194                             .span_label(e.span, "labeled blocks cannot be `continue`'d")
 195                             .span_label(block.span, "labeled block the `continue` points to")
 196                             .emit();
 197                         }
 198                     }
 199                     Err(hir::LoopIdError::UnlabeledCfInWhileCondition) => {
 200                         self.emit_unlabled_cf_in_while_condition(e.span, "continue");
 201                     }
 202                     Err(_) => {}
 203                 }
 204                 self.require_break_cx("continue", e.span)
 205             }
 206             _ => intravisit::walk_expr(self, e),
 207         }
 208     }
 209 }
 210
 211 impl<'a, 'hir> CheckLoopVisitor<'a, 'hir> {
 212     fn with_context<F>(&mut self, cx: Context, f: F)
 213     where
 214         F: FnOnce(&mut CheckLoopVisitor<'a, 'hir>),
 215     {
 216         let old_cx = self.cx;
 217         self.cx = cx;
 218         f(self);
 219         self.cx = old_cx;
 220     }
 221
 222     fn require_break_cx(&self, name: &str, span: Span) {
 223         let err_inside_of = |article, ty, closure_span| {
 224             struct_span_err!(self.sess, span, E0267, "`{}` inside of {} {}", name, article, ty)
 225                 .span_label(span, format!("cannot `{}` inside of {} {}", name, article, ty))
 226                 .span_label(closure_span, &format!("enclosing {}", ty))
 227                 .emit();
 228         };
 229
 230         match self.cx {
 231             LabeledBlock | Loop(_) => {}
 232             Closure(closure_span) => err_inside_of("a", "closure", closure_span),
 233             AsyncClosure(closure_span) => err_inside_of("an", "`async` block", closure_span),
 234             Normal | AnonConst => {
 235                 struct_span_err!(self.sess, span, E0268, "`{}` outside of a loop", name)
 236                     .span_label(span, format!("cannot `{}` outside of a loop", name))
 237                     .emit();
 238             }
 239         }
 240     }
 241
 242     fn require_label_in_labeled_block(
 243         &mut self,
 244         span: Span,
 245         label: &Destination,
 246         cf_type: &str,
 247     ) -> bool {
 248         if !span.is_desugaring(DesugaringKind::QuestionMark) && self.cx == LabeledBlock {
 249             if label.label.is_none() {
 250                 struct_span_err!(
 251                     self.sess,
 252                     span,
 253                     E0695,
 254                     "unlabeled `{}` inside of a labeled block",
 255                     cf_type
 256                 )
 257                 .span_label(
 258                     span,
 259                     format!(
 260                         "`{}` statements that would diverge to or through \
 261                                 a labeled block need to bear a label",
 262                         cf_type
 263                     ),
 264                 )
 265                 .emit();
 266                 return true;
 267             }
 268         }
 269         false
 270     }
 271     fn emit_unlabled_cf_in_while_condition(&mut self, span: Span, cf_type: &str) {
 272         struct_span_err!(
 273             self.sess,
 274             span,
 275             E0590,
 276             "`break` or `continue` with no label in the condition of a `while` loop"
 277         )
 278         .span_label(span, format!("unlabeled `{}` in the condition of a `while` loop", cf_type))
 279         .emit();
 280     }
 281 }